Variable Interest Entities (Summary of Trusts' Income Statement) (Details) - Variable Interest Entity, Not Primary Beneficiary - Southern California Edison - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Trust I
Variable Interest Entity
Dividend income		$ 7
Dividend distributions		7
Trust II
Variable Interest Entity
Dividend income	$ 5	5
Dividend distributions	5	5
Trust III
Variable Interest Entity
Dividend income	4	4
Dividend distributions	4	4
Trust IV
Variable Interest Entity
Dividend income	4	4
Dividend distributions	4	4
Trust V
Variable Interest Entity
Dividend income	4	4
Dividend distributions	4	$ 4
Trust VI
Variable Interest Entity
Dividend income	6
Dividend distributions	$ 6